1. Field of the Invention
The present invention relates to a vacuum processing method, a vacuum processing apparatus, a semiconductor device, using a high frequency power, which is used for forming a deposited film, etching, and so on, in semiconductor device, electrophotographic photosensitive members, image input line sensors, photographic devices, photovoltaic devices, and so on.
2. Related Background Art
As for a vacuum processing method used when creating semiconductor devices, electrophotographic photosensitive members, image input line sensors, photographing devices, photovoltaic devices, other various electronic elements, optical elements, and so on, many methods such as a vacuum evaporation method, a sputtering method, an ion plating method, a thermal CVD method, a photo-chemical vapor deposition method and a plasma CVD method are known, and apparatuses therefor are put into practice. Among others, a plasma process using a high-frequency power has various advantages, that is, its discharge is highly stable, it can be used for formation of deposited films using various materials and etching, and it can also be used for formation of insulating materials of oxide films and nitrided films, for instance. As a suitable use of the plasma process, formation of hydrogenated amorphous silicon deposited films for electrophotography, and so on, can be named for instance, and commercialization of this plasma process is rapidly underway today with various apparatuses for that purpose also proposed.
In addition, various attempts to make a variety of improvements are further made by changing the method of supplying this high-frequency power.
For instance, Japanese Patent Application Laid-Open No. 56-45760 discloses a technology wherein a plurality of power supplies of different frequencies (13.56 MHz and 400 kHz just as an example) are applied as the power supplies for exciting a reaction gas to the same electrode to excite the reaction gas so as to form a deposited film on a substrate to be processed.
In addition, Japanese Patent Application Laid-Open No. 60-160620 (corresponding to EP 0149089) discloses a plasma reactor apparatus having a constitution for supplying the high-frequency power of 10 MHz or more and the high-frequency power of 1 MHz or less (13.56 MHz and 100 kHz just as an example) to the same electrode.
Furthermore, Japanese Patent Application Laid-Open No. 62-188783 discloses a method for manufacturing an electrostatic latent image holding member, whereby a modulation frequency power having a low-frequency AC power (20 Hz to 1 MHz) and a high-frequency AC power (1 MHz to 100 GHz) superimposed is supplied to the electrode so as to speed up film formation by no longer requiring a heater and superpose an amorphous semiconductor layer on the substrate.
On the other hand, in recent years, there is a report on the plasma CVD method using the high-frequency power supply of a higher frequency (Plasma Chemistry and Plasma Processing, Vol. 7, No. 3, (1987), pp. 267 to 273), which is receiving attention in showing a possibility of improving a deposition rate without reducing performance of the deposited film by rendering a discharge frequency higher than the conventional 13.56 MHz. It is expected that this method will allow cost reduction and higher quality of products to be simultaneously accomplished.
For instance, Japanese Patent Application Laid-Open No. 6-287760 (corresponding to U.S. Pat. No. 5,534,070) discloses an apparatus and a method for performing the plasma CVD using the frequency of a VHF band of which frequencies are from 30 MHz to 300 MHz or less, useable for formation of an amorphous silicon light-receiving member for electrophotography.
Moreover, as an example of a combination of the above-mentioned method of using the two types of the high-frequency powers and the method of applying the high-frequency power of a higher frequency, Japanese Patent Application Laid-Open No. 7-074159 discloses the technology wherein, in a plasma processing method for cleaning the substrate, the high-frequency power of a relatively high frequency and the high-frequency power of a relatively low frequency (high-frequency powers of 60 MHz and 400 kHz just as an example) are supplied to the electrode for mounting the substrate, and a power value of the power of the relatively low frequency is changed so as to control a self-bias voltage for determining collision energy of a plus ion.
In addition, Japanese Patent Application Laid-Open No. 7-321105 discloses the technology wherein, in the method for manufacturing a semiconductor device, the power supply for supplying the high-frequency power of a relatively high frequency in the range of 10 MHz to 1 GHz (high-frequency power of 13.56 MHz just as an example) and the power supply for supplying the high-frequency power of a relatively low frequency in the range of 300 kHz to 500 kHz (high-frequency power of 400 kHz just as an example) are used to form a layer insulation film.
Moreover, Japanese Patent Application Laid-Open No. 9-321031 (corresponding to U.S. Pat. No. 5,891,252) discloses a plasma processing apparatus having a constitution for simultaneously applying a first high-frequency power of a UHF band (300 MHz to 1 GHz) and a second high-frequency power that is different therefrom by twice or more.
The conventional methods and apparatuses as mentioned above allow good deposited film formation, that is, good vacuum processing to be performed. However, the level of the market demand for such products made using the vacuum processing is becoming higher day after day, and so the vacuum processing method, vacuum processing apparatus, semiconductor device and manufacturing method thereof capable of implementing higher quality and cost reduction are required in order to meet this demand.
For instance, in the case of an electrophotographic apparatus, the demands for an improved copying speed, a higher image quality and lower prices are very strong, and in order to implement these, it is essential to improve the characteristics of the photosensitive member, that is, to be more specific, chargeability, sensitivity, and so on, to suppress image defects appearing as white dots or black dots on the image that are caused by a faulty structure inside the photosensitive member and to reduce the production costs for the photosensitive member. In addition, as for digital electrophotographic apparatuses and color electrophotographic apparatuses that are remarkably widespread in recent years, it is required more strongly than before, as they are often used to copy photos, pictures and design drawings in addition to writings, to form a film of a large area of which film thickness and film quality are both uniform in order to reduce a photomemory of the photosensitive member and also to reduce image density unevenness.
While optimization of a deposited film lamination constitution and so on are conducted aiming at improvement in such photosensitive member characteristics and reduction of photosensitive member production costs, improvement in the aspect of the vacuum processing method is also strongly desired at the same time.
In these circumstances, the present status is that there is still room left for improvement as to enhancement in vacuum processing characteristics and reduction of the vacuum processing costs in the aforementioned conventional vacuum processing method and semiconductor device manufacturing method.
As already mentioned, it is possible to accomplish improvement in the vacuum processing speed and improvement in the vacuum processing characteristics by using the high-frequency power of the frequency in the VHF band or in the vicinity thereof to generate plasma and to perform the vacuum processing, and earnest research is conducted for that purpose. In the case of using the high-frequency power in such a frequency band, however, a wavelength of the high-frequency power in a reaction container becomes as long as the reaction container, a high-frequency electrode, a substrate or a substrate holder, and so on, and so the high-frequency power is apt to form a standing wave in the reaction container. This standing wave causes the power to be strong or weak at each location in the reaction container, thus, leading to different plasma characteristics. Consequently, it was difficult to render the vacuum processing characteristics further uniform in a broad range.
In addition, in the case of the device having a thick film thickness such as the electrophotographic photosensitive member, there were cases where the state of the plasma changes as the film was deposited so that distribution of characteristics in an in-plane direction of the substrate became different in the film thickness direction resulting in nonuniformity of the film quality or change of the film quality itself in the thickness direction.
Such nonuniformity is a serious problem in the case of forming a crystalline or non-single crystalline functional deposited film used not only for the electrophotographic photosensitive member but also for the photovoltaic devices, image input line sensors, imaging devices and so on. In addition, the same processing unevenness will arise in plasma processing processes such as dry etching and sputtering in the case of rendering the discharge frequency higher, which will become a serious problem in practice if it remains as it is.
Although various improvements have been made in the electrode's shape, the form of applying the high-frequency power and so on in order to reduce such processing unevenness and render the uniformity higher, it has been by no means easy to maintain compatibility between the uniformity of the film thickness and that of the film quality and to acquire the deposited film having good film quality while maintaining the uniformity of the film thickness.
In particular, in the case of making an attempt to acquire the uniformity by a structural improvement in the electrode's shape and so on, as to a lamination device having a plurality of layer areas, a method that is effective in a specific layer area may not be sufficiently effective in another layer area, and so a handy and effective method for maintaining the uniformity in the case of the device having a plurality of layer areas made under different layer forming conditions has been sought.
As means for solving such problems, it is thinkable to simultaneously supply a plurality of the high-frequency powers of different frequencies in the reaction container. While a plurality of standing waves of different wavelengths according to the respective frequencies are thereby formed in the reaction container, the plurality of standing waves are synthesized since they are simultaneously supplied and no definite standing wave is formed as a consequence. Based on this idea, the effect of suppressing the standing waves can be obtained with different frequencies of a plurality of high-frequency powers irrespective of their values. For instance, it is thinkable that use of the technology disclosed by Japanese Patent Application Laid-Open No. 60-160620 will suppress the standing waves of the high-frequency powers in the reaction container so as to improve the uniformity of the vacuum processing.
However, as a result of conducting an experiment on the uniformity of the vacuum processing characteristics by using the technology disclosed by Japanese Patent Application Laid-Open No. 60-160620, the inventors hereof could certainly improve the uniformity to a certain level but could not acquire the uniformity level that is required in recent years. To be more specific, it became evident that, even by using a power supply method that is rendered uniform in terms of field strength, the nonuniformity remains to a certain extent in the actual vacuum processing.